AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
Students should be able to describe the nature of the compounds formed…
Full specification wording
Group 7: Students should be able to describe the nature of the compounds formed when chlorine, bromine and iodine react with metals and non-metals.
When chlorine, bromine or iodine reacts with a metal, the halogen gains one electron from the metal atom.
Checked against the AQA 8464 specification (opens in a new tab) on .
- Point 2 of 7
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
When chlorine, bromine or iodine reacts with a metal, the halogen gains one electron from the metal atom. The metal loses electrons and becomes a positive ion, while the halogen becomes a negative ion. The oppositely charged ions attract strongly, forming an ionic compound. For example, sodium reacts with chlorine to form sodium chloride, NaCl, containing Na⁺ and Cl⁻ ions. When a halogen reacts with a non-metal such as hydrogen, the atoms share electrons instead. Hydrogen and chlorine share a pair of electrons to form hydrogen chloride, HCl, a simple covalent molecule. So the nature of the compound depends on the other element: ionic with metals, covalent with non-metals. In both cases the halogen achieves a full outer shell of eight electrons, which is why it reacts.
What earns the marks
- Halogens react with metals to form ionic compounds in which the halogen becomes a negative ion, for example Cl⁻.
- The metal atom loses electrons to become a positive ion, for example Na⁺, and the ions attract to form the compound.
- Halogens react with non-metals such as hydrogen to form covalent compounds in which electrons are shared.
- Hydrogen chloride, HCl, is a covalent molecule formed when hydrogen and chlorine share a pair of electrons.
- In both ionic and covalent compounds, the halogen atom gains or shares electrons to complete an outer shell of eight.
Common mistakes and how to put them right
Saying halogens form covalent compounds with all elements.
Put it right by stating they form ionic compounds with metals and covalent compounds with non-metals.
Writing sodium chloride as molecules of NaCl rather than as a lattice of Na⁺ and Cl⁻ ions.
Put it right by describing the ionic lattice.
Forgetting that the halogen becomes a negative ion in an ionic compound.
Put it right by showing Cl gaining one electron to form Cl⁻.
Exam tips
- Name the type of bonding first, then explain the electron transfer or sharing that produces it.
- Use correct ion symbols with superscript charges, such as Na⁺ and Cl⁻, when describing ionic compounds.
- Give one metal example and one non-metal example, such as sodium chloride and hydrogen chloride, to cover both parts of the statement.
Try the lesson
The start of the Group 7: Students should be able to describe the nature of the compounds formed when chlorine, bromine and iodine react with metals and non-metals. lesson, made from checked teaching notes for this specification point.
Have a go first
When sodium reacts with chlorine, what type of compound is formed?
Listen
When chlorine, bromine or iodine reacts with a metal, the halogen gains one electron from the metal atom. The metal loses electrons and becomes a positive ion, while the halogen becomes a negative ion. The oppositely charged ions attract strongly, forming an ionic compound. For example, sodium reacts with chlorine to form sodium chloride, NaCl, containing Na⁺ and Cl⁻ ions. When a halogen reacts with a non-metal such as hydrogen, the atoms share electrons instead. Hydrogen and chlorine share a pair of electrons to form hydrogen chloride, HCl, a simple covalent molecule. So the nature of the compound depends on the other element: ionic with metals, covalent with non-metals. In both cases the halogen achieves a full outer shell of eight electrons, which is why it reacts. A strong answer earns marks for these points. Halogens react with metals to form ionic compounds in which the halogen becomes a negative ion, for example Cl⁻. The metal atom loses electrons to become a positive ion, for example Na⁺, and the ions attract to form the compound. Halogens react with non-metals such as hydrogen to form covalent compounds in which electrons are shared. Hydrogen chloride, HCl, is a covalent molecule formed when hydrogen and chlorine share a pair of electrons. A common slip: Saying halogens form covalent compounds with all elements. Instead, stating they form ionic compounds with metals and covalent compounds with non-metals. Exam tip: Name the type of bonding first, then explain the electron transfer or sharing that produces it.
Key words
Say what each word means before you turn the card.
Ionic bonding
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Covalent bonding
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Electron transfer and sharing
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Halogen reactivity
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See every definition
- Ionic bonding
- The oppositely charged ions attract strongly, forming an ionic compound when a halogen reacts with a metal.
- Covalent bonding
- When a halogen reacts with a non-metal such as hydrogen, the atoms share electrons instead.
- Electron transfer and sharing
- The metal loses electrons and becomes a positive ion, while the halogen becomes a negative ion; with non-metals the atoms share electrons instead.
- Halogen reactivity
- The halogen achieves a full outer shell of eight electrons, which is why it reacts.
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